The Rotterdam Study is a prospective cohort study that has been ongoing since 1990 in the city of Rotterdam, the Netherlands, among 7983 people aged 55 years or older. One part of the study targets neurological diseases, others deal with cardiovascular, ophthalmological, and endocrine diseases. The findings of the Rotterdam Study have been presented in some . Here we give the reasons for the study and its design, and present a summary of what has been learned about the frequencies and causes of neurological diseases. Perhaps the most important message from the Rotterdam Study is the great potential for prevention or postponement of neurological diseases in elderly people. The time for preventive nihilism is over.